Petrogenesis of ore-bearing porphyry from the Tangjiaping porphyry Mo deposit, Dabie orogen: Zircon U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopic constraints
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Felsic
Molybdenite
Petrogenesis
Geochronology
Quartz monzonite
Magmatic zircons in two samples of quartz monzonite pluton from southern Nanjiao,Zhoukoudian,Beijing,were analysed using LA-ICP-MS technique,yielding206Pb/238U ages of(133.0+2.0/-5.0) Ma and(134.0+1.0/-5.0) Ma,with weighted average age of(134.0+1.0/-2.0) Ma.This provides constraints that the quartz monzonite granitoid is of the late Yanshanian intrusion,and that the slip structure along the parallel unconformity of the Carboniferous on the Ordovician strata should have occurred no later than ~134 Ma.The quartz monzonite plutons in the Najiao area intruded at the peak of lithosphere destruction of the northeastern China.
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The mid-Miocene Aztec Wash pluton is divisible into a relatively homogeneous portion entirely comprising granites (the G zone, or GZ), and an extremely heterogeneous zone (HZ) that includes the products of the mingling, mixing and fractional crystallisation of mafic and felsic magmas. Though far less variable than the HZ, the GZ nonetheless records a dynamic history characterised by cyclic deposition of the solidifying products of the felsic portion of a recharging, open-system magma chamber.
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Fractional crystallization (geology)
Igneous differentiation
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The Cretaceous-Palaeogene alkaline province, mainly located in the Kırşehir Block, extends E-W for some 300 km in Central Eastern Anatolia. The Dumluca, Murmana, Karakeban and Çaltı plutons constitute the easternmost part of the province. These plutons have introsive contacts with the Cretaceous Divriği ophiolitic melange and, except Karakeban, are associated with huge iron deposits. The Ypresian-Lutetian sediments unconformubly overly them. The four studied plutons belong to two completely different types of magmatic assocsiation, based on petrographic and geochemical (mainly major elements and REE) fetures. The dominant association comprises three plutons (Dumluca, Murmana, Karakeban) and is rather uniformly represented within each of them. These three plutons have a bimodal character evidenced by the coexistence of two groups of rocks, one mafic and the other felsic. The dominant felsic group, mainly composed of Na-rich and Ca-poor quartz monzonites and monzonites (Murmana, Dumluca), may also include syenites, quartz syenites, adamellites and granites (Karakeban). This group displays a cafemic alkaline over staurated trend, usually magnesian (Dumluca and Murmana) and common (Karakeban). The mafic group is mainly made up Na-rich and Ca-poor gabbros/diorites, monzogabbros/monzodiorites, rather often silica-undersaturated. This group represents a cafemic alkaline saturated to undersaturated trend either ferriferous (Karakeban) or magnesian (Dumluca) or or common (Murmana). Mafic dykes, cutting through the felsic rocks, belong to the same mafic group. These three plutons represent a composite alkaline association and the same type of association characterizes also each individual pluton. Field, petrographic and geochemical data suggest that the felsic group has not been derived from the mafic one by crystal fractionation, but that the two coevial groups may have interacted with each other. The subordinate association is represented by Çaltı pluton. This homogenous pluton, tonalitic and gronodioritic in composition, corresponds to a cafemic calc-alkaline association,with slight magnesian affinity. Such a coexistence of two quite different magmatic associations in the Divriği region has already been reported in the western part of Kırşehir Block. It shows that the alkaline character is restricted to only part of the plutons located in this block and may suggest that several successive magmatic events, related to quite different geodynamic conditions, occured in this domain. In this framework, the Dumluca, Murmana and Karakeban plutons are thougth to be derived from two different magma sources. One of them is mantle related mafic magma generated in a post-collisional lithospheric attenuation environment which accordingly caused to melt the lower parts of the continental crust forming the felsic magma source. This collisional event is attributed to the juxtaposition of the Pontide and Anatolide plates in the pre-Maastrictian time. The Çaltı pluton, representing different mineralogy and chemistry, should be solidified from the collision related and calcalkaline another hybrid magma source due especially to intruding the already obducted Divriği ophiolitic melange. Isotopic and geochronological data would be particularly helpful to better constrain this magmatic history.
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Aztec Wash pluton, a 50 km[sup 2] intrusive complex in the northern Eldorado Mountains, was emplaced ca. 16 Ma (Faulds et al., 1990) during extension within the Colorado River Corridor. The pluton displays extreme compositional variability, ranging from olivine gabbro (ca. 50 wt% SiO[sub 2]) to highly evolved aplite (76% SiO[sub 2]). Most of the intrusion is medium grained, homogeneous granite (ca. 72% SiO[sub 2]), but 1/3 is highly heterogeneous and dominated by mafic to intermediate rocks; a 6 [times] 3km, N-S mafic zone almost bisects the pluton. Well-displayed magma mingling and late mafic and felsic dikes verify the coexistence of mafic and felsic melts. Hornblende barometry indicates that the entire exposed portion of Aztec Wash pluton was emplaced at very shallow depth (
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Field relations and geochemistry indicate that Aztec Wash pluton had a complex, open-system history. The tilted pluton represents a 2.5 km thick chamber that was recharged with both felsic and mafic magma. The lower portion is highly heterogeneous, with mafic sheets; cumulates; hybrid rocks; mafic, felsic, and composite dikes; and sheets and pods of granite (heterogeneous [H] zone). The upper part is granite that is generally homogeneous in texture and geochemistry (granite [G] zone). At the base of the G zone, a discontinuous zone (buffer [B] zone) records interaction between the G and H zones. Complexity of the H zone makes detailed reconstruction of magma chamber history difficult, and the relatively homogeneous G zone appears to offer few clues about the evolution of the pluton or the interaction between the felsic and underlying more mafic magmas. Accessory mineral textures, zoning, and assemblages in the G zone, however, are far from homogeneous and provide clear evidence for fluctuating conditions that elucidates magma chamber history.
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The Himekami pluton is a complex of mafic rocks and their differentiated felsic rocks, which belong to shoshonite rock association. The pluton is devided into three bodies: South pluton, North pluton and Shiroishi pluton. The South pluton, consisting mainly of monzonite, monzogabbro, quartz monzonite and quartz monzodiorite, is classified genetically into four groups of mafic and felsic rocks. Each rock group accompanies a few amounts of xenolithic mass of cumulated, ultramafic rocks and melagabbro. The North pluton is a zoned pluton of quartz monzonite, granite and granodiorite. The Shiroishi pluton is a leucocratic tonalite-granodiorite.
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Abstract The Baishiding molybdenum deposit is located in the Central‐Middle Guangxi depression zone of the South China Caledonian fold zone. Orebodies occur as quartz‐molybdenite veins within the Guiling monzonite pluton and arkosic quartz sandstone of Zhengyuanling Group in the northeastern Guangxi. They are NEE‐trending with a dip angle of 75–80°. Zircon SHRIMP U‐Pb geochronologic analyses of the Guiling monzonite show age of 424.4 ± 5.6 Ma. It indicates that the Guiling monzonite was emplaced in Silurian. The ore minerals in quartz‐molybdenite veins contain molybdenite, pyrite, chalcopyrite and scheelite. Six molybdenite samples yield Re‐Os ages between 433.3 ± 6.3 Ma and 417.2 ± 5.7 Ma, with a weighted mean age of 424.6 ± 5.7 Ma, which agrees with the zircon age of the Guiling monzonite pluton. It suggests that the deposit was formed in the Silurian, not the Jurassic as previously thought. The Baishiding deposit is the only Silurian molybdenum deposit so far recognized in the South China. It was probably formed in a crustal shortening setting along the continental margin in the Silurian.
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Abstract Mount Dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the Dromedary igneous complex in southeastern New South Wales. The pluton exhibits a striking arrangement of petrographically, but not always chemically, distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre. The rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship. Minor compositional discontinuities between zones, together with observed and inferred minor intrusive zone boundaries, suggest that each zone has to some extent evolved independently. Negative Eu anomalies in REE abundance patterns show that some of the zones have been affected by fractionation of feldspar, but complementary accumulates are not found at the present levels of exposure. The pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and/or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma. The parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust.
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Fractional crystallization (geology)
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